This is because Original Elemental HERO monsters are a subtype of HERO monsters. They are considered both "HERO" and "Elemental HERO" by the game's rules.
Here's a breakdown:
* HERO: This is a broader category that includes all monsters with the "HERO" type, including Original Elemental HERO, Vision HERO, and other HERO types.
* Elemental HERO: This is a sub-type of the HERO monster category that includes all monsters with the "Elemental HERO" type. Original Elemental HERO monsters are considered Elemental HERO monsters.
Therefore, if a card's effect mentions "HERO" or "Elemental HERO", you can use Original Elemental HERO monsters to fulfill the requirement.
For example, if a card says "Activate this card by sending 1 "HERO" monster from your hand to the graveyard", you can use an Original Elemental HERO monster to activate the effect.